It’s August in Louisville, Ky., and my alarm goes off at 5:40 a.m. Time for my morning run with my four-legged running buddy, Julep. After I do some light stretching, we’re pounding the pavement by 6 a.m. to get a 5-mile run in.
I choose to exercise before work because it’s (slightly) cooler compared to later in the day when the sun is shining bright. Cooler temperatures benefit me and Julep, but in different physiological ways.
When humans are at rest, almost half of our blood volume goes to organs in the gut, such as the kidneys and intestines. Once we start exercising, blood flow increases to the exercising muscles, such as the heart and hamstrings. Blood flow to the gut decreases at the same time.
If it’s over 80 degrees Fahrenheit, a large amount of blood shifts toward the skin, where sweat glands are located. At the same time, the autonomic nervous system causes these sweat glands to “turn on” and secrete water and minerals called electrolytes. When air travels across the wet skin, the water evaporates, which releases internal heat and cools the body.
Julep, my 3-year-old German shorthaired pointer, has maximum energy. As she starts to exercise, blood flow increases and shifts to her exercising muscles, too. In dogs, blood flow also increases to the head and paws during physical activity. There are two reasons for this: First, dogs have no sweat glands except in their foot pads. Second, they use their mouth and tongue to pant, which evaporates water and releases heat. That is why it is important for dogs to also be properly hydrated—their mucous membranes in their mouth then stay wet and can cool them off. Running before sunrise is also beneficial for dogs because it decreases the chance of a foot pad injury from scorched pavement.
Here are a few more things to keep in mind before heading out to exercise with your pup: Some breeds with short noses and flat faces—such as chow chows and boxers—can’t release heat as well as other breeds. Also, try to avoid heavy exercise during peak daylight hours if your dog has a darker or thicker coat because they absorb more heat.
Becoming acclimated to the heat and staying hydrated can improve human and canine exercise capacity and make exercising with your pup a safe and enjoyable experience for everyone. Happy trails!
Amanda Jo LeBlanc, PhD, is a cardiovascular physiologist and an associate professor at the University of Louisville School of Medicine. She studies microvascular function in aging and is a former collegiate cross-country and track athlete at Indiana University. She now enjoys running much slower with her dog, Julep.